I would like to store the user's birth YEAR (not the complete Date of Birth). I have an optional field called cb_dob_year for this, which users fill in when registering.

If the user uses a social network, e.g. Facebook, to register, he/she would not provide his/her birth YEAR. However, some social networks provide the DATE of birth. I mapped the social network field to an optional field called cb_dob.

In the case where the user uses a social network to register, I want to use the birth date value, which is in cb_dob to fill in the birth year in cb_dob_year. Using db terminology, I need to create some sort of a trigger to extract the year value from cb_dob and store it in cb_dob_year. Is this at all possible using some CB plugins?